Round 16 sees Biarritz take the Top 14's best defence on the road to Toulouse where they will face the championship's best attack.
With Toulouse and Clermont well clear of the rest, a four-way battle for the last two semi-final spots has emerged with Perpignan and Castres snapping at the heels of Stade Français and Biarritz.
At the opposite end of the table Auch and Dax face off in a golden opportunity for Dax to close the gap on Albi in the race to avoid relegation.
Fixtures
Friday 28 March
Stade Toulousain v Biarritz Olympique
Saturday 29 March
Bayonne v Stade Français
Clermont Auvergne v Albi
Auch v Dax
Castres v Montpellier
Brive v Montauban
Bourgoin v Perpignan
Table after Round 15
1 Stade Toulousain 58
2 Clermont Auvergne 57
3 Stade Français 44
4 Biarritz Olympique 41
5 Perpignan 40
6 Castres Olympique 40
7 Montauban 35
8 Bourgoin 34
9 Bayonne 33
10 Montpellier 30
11 Brive 27
12 Albi 25
13 Dax 20
14 Auch 10
Stade Toulousain v Biarritz Olympique
It's D-day for Biarritz. With only one point separating the Basque side from Perpignan and Castres, it's time to prove they deserve a place in the semi-finals.
They might have the best defensive record in the Top 14, but their attack has failed to convince.
BO haven't scored a single offensive bonus point this season, but they'll have to score some tries if they want to be competitive against a club that hasn't lost at home since November 2006.
For all of Biarritz's defensive prowess, you can beat your bottom dollar that the best attack in France will have the scoreboard ticking over on their home ground.
Maxime Médard and Vincent Clerc are first and third respectively on the league's try-scoring list, and with all of Toulouse's big guns rested up after their much publicised absence last weekend, that Biarritz defence will do well not to turn into cannon fodder.
Biarritz have been plagued by injuries and seem to be on downward spiral. Of the four clubs in the race for a semi-final spot, they have the hardest fixtures by far with visits to Toulouse, Montauban, Perpignan and Paris still to come.
They will be looking for big performances from big-name players. Jerome Thion was a monster in the rain to lead the BO pack to victory last weekend and Dimitri Yachvilli's boot has become an object of worship on the south-west coast.
Toulouse, at home, make for daunting opposition. Spoilt for choice when he actually chooses to choose his best team, Guy Novès is able to line-up a Test capped player at every position most weekends.
How many teams in world rugby can afford to leave a player of Byron Kelleher's class on the bench?
Toulouse have actually conceded less tries than Biarritz this season and the Basques' visit to Ernest Wallon will be a warm-up to Toulouse's Heineken Cup quarter-final against Cardiff at the far bigger Stade Municipal a week later.
The teams have met sixteen times and Toulouse have won all but twice, including the last five meetings.
Biarritz lost 18-6 at home toToulouse in Round 3 and with all of Toulouse's stars set to return to action this weekend, a repeat result is the most likely outcome.
Date: Friday 28 March
Venue: Ernest Wallon
Kick-off: 20:30
Bayonne v Stade Français
Bayonne started the week with the destabilising news that manager Jean-Pierre Elissalde and coaches Xavier Péjéma and Jean-François Beltran will be given their marching orders at the end of the season.
The home side will once again be relying heavily on their points-scoring machine Richard Dourthe, who is the third highest scorer in the championship with 143 points this season.
Even if Toulouse didn't field their best side, beating the championship leaders 29-0 in front of 80,000 people could only have done the world of good for Stade Français's confidence.
After being winless for a month, last weeks spectacle would have put a spring in the step of a team capable of beating anyone on their day.
The defending champions have arguably the easiest draw of the four teams in the semi-finals race and will probably be concentrating more on catching up to the leaders than worrying about those behind them.
However, it's not all good news for the Parisians. France fly-half David Skrela has a thigh injury that could see him sidelined for as long as two months.
Date: Saturday 29 March
Venue: Jean Dauger
Kick-off: 15:05
Clermont Auvergne v Albi
Depending on what team Clermont choose to send out against their lowly opponents, Round 16 could see Clermont break the 50-point barrier for the third week in succession.
As if Clermont's French and South African stars weren't enough to contend with, Albi will have to try come up with some way of stopping Fijian Napolioni Nalaga who has scored eight tries in five games - two in each of his last three appearances!
Add to that Australian Brock James, who is the championship's top place-kicker (150 points), and you've got a recipe for Abli tears.
Date: Saturday 29 March
Venue: Marcel Michelin
Kick-off: 17:30 (16:30 GMT)
Auch v Dax
This is a true relegation battle as last hosts second last. Auch's fate is has practically already been sealed but a win for Dax would see them erase the gap between them and 12th placed Albi, who are almost certain to lose in Clermont.
Neither team has recorded an away win this year but this is as good a chance to do so as Dax will ever have. It's now or never for Dax who will want to repeat their 16-6 victory of earlier in the season.
Date: Saturday 29 March
Venue: Moulias
Kick-off: 17:30 (16:30 GMT)
Castres Olympique v Montpellier
Castres have a monumental month ahead of them. They will face four of the top five away from home - hosting only Toulouse (!) -which makes the likelihood of them qualifying for the semi-finals a long shot.
They are, however, very well placed to qualify for the next edition of the Heineken Cup and Montpellier will be direct competition in that race.
The home side will fancy their chances against a Montpellier side in freefall.
The absence of four of their key players during the Six Nations no doubt played a large part in their recent decline but a full strength team nevertheless took a 42-point hammering at home to Clermont last week.
Australian Steve Kefu has transformed the Castres midfield, and has played a large part in Castres' four-game winning streak.
A good day with the boot could see Castres full-back Romain Teulet top the championship's point scoring classification (he is currently second, just one behind leader Brock James).
Following Perpignan's example, Montpellier spent three days at altitude mid-week at the Pyrenean spa/resort of Falgos on a soul-searching mission.
They might have come back with more red blood cells but the mountain air didn't do anything for the injuries of the French international half-back combination of François Trinh-Duc and Julien Tomas who will both be sidelined for three weeks.
Trinh-Duc has a rib injury while Tomas has pulled a calf muscle. South African centre Rickus Lubbe will also be missing from the Montpellier midfield with a knee injury. Kefu will be rubbing his hands in anticipation.
Date: Saturday 29 March
Venue: Pierre-Antoine
Kick-off: 17:30 (16:30 GMT)
Brive v Montauban
When Brive visited Montauban four months ago, they were beaten by 30 points. They will certainly be expecting to do better at home.
Montauban are seventh, the same position they finished in last year. Relatively safe from the threat of relegation, the question remains whether they can lift their game to compete for a place in Europe.
Their trip to Brive will give a good indication whether or not they have fallen foul of the comfort of their position.
Brive, on the other hand, are far from comfortable. One or two bad results and they could be dragged into the relegation scrap, so their ambitions against Montauban go further than simple revenge.
Montauban received good news on Wednesday when new French international flanker Ibrahim Diarra extended his contract for two more seasons.
Date: Saturday 29 March
Venue: Amedée-Domenech
Kick-off: 17:30 (16:30 GMT)
Bourgoin - Perpignan
Perpignan have made an amazing U-turn in form over the past few weeks.
Given their current form and a very favourable draw for the last half of the season, the Catalans are odds-on favourites to make the semi-finals (they have away games to lowly Dax and Auch while their main rivals - Castres, Biarritz and Stade Français - must travel to Aimé-Giral).
The team from the Mediterranean coast will further be buoyed by the news that former France A winger Farid Sid will return to Perpignan from Brive next season.
However, before they get too excited, they have the difficult task of travelling to Bourgoin.
Many a team has come unstuck at Pierre-Rajon this season, including Toulouse, Biarritz and Montpellier.
It would be hard to imagine that the teams will repeat November's 3-3 draw, but a close game is still very likely.
Perpignan centre David Marty is in fantastic form at the moment and will be looking to repeat his double-try scoring efforts of last week's win over Albi.
French international scrum-half Morgan Parra has been in equally good form and will be eager to show his leadership skills in marshalling the Bourgoin pack.
Date: Saturday 29 March
Venue: Pierre-Rajon
Kick-off: 20:30 (19:30 GMT)